1. Field of the Invention
The present invention relates to a zoom lens, and particularly relates to a zoom lens suitably used in a projector.
2. Description of the Related Art
A liquid crystal projector is a device capable of projecting an image generated by a personal computer, a video apparatus, and the like on a large screen, and is used in various situations including a presentation and a meeting. In a projection optical system used in the liquid crystal projector, it is desired to secure, first, as a configuration, a front lens diameter that can be housed in a projector body, and a long back focus for securing a space for a color combining prism arranged between the projection optical system and a liquid crystal panel. Further, to uniform the contrast characteristic within a liquid crystal panel screen, a telecentric optical system is desired, in which a pupil at a liquid crystal panel (reduction conjugate plane) side is positioned at an infinite distance. Further, as a performance, favorable reduction of various aberrations in the entire zoom range is required.
In the past, as a type of the telecentric projection optical system, there has been a negative lead type zoom lens, in which a lens unit having negative refractive power is located at the forefront, and a large number of negative lead type wide-angle zoom lenses that secure the long back focus have been discussed.
However, the negative lead type zoom lenses have a problem of increasing in size when seeking a telephoto performance while minimizing an increase in size of the diameter.
Meanwhile, a positive lead type zoom lens, in which a lens unit having positive refractive power is located at the forefront, is discussed in Japanese Patent Application Laid-Open No. 2003-287680.
Japanese Patent Application Laid-Open No. 2003-287680 discusses a zoom lens includes, in order from a screen side (enlargement conjugate side) to a liquid crystal panel side (reduction conjugate plane side), a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having negative refractive power, a fourth lens unit having positive refractive power, a fifth lens unit having positive refractive power, and a sixth lens unit having positive refractive power. During zooming from a wide-angle end to a telephoto end, the second lens unit moves to the reduction conjugate side, the third lens unit, the fourth lens unit, and the fifth lens unit move to the enlargement conjugate side.